Within the last few decades, numerous rapid lateral flow assays have been developed and implemented for determining the presence or absence of specific analytes in bodily fluids, such as in blood, urine, saliva; on the surface of objects in the environment; and in other dried and aqueous substances. Multiple patents have been awarded for the development of such lateral flow assay techniques (U.S. Pat. Nos. 4,855,240, 5,120,643, 5,569,608, 5,591,645, 5,656,503, 6,303,081, 7,192,555, and WO/1999/006827). Rapid lateral flow assays are commonly used to detect diseases, drugs, hormones, bacteria, viruses, and biomarkers in human bodily fluids (1-3). Published scientific literature has demonstrated the wide application of lateral flow assays to screen human urine, saliva, and/or blood/serum/plasma for testing or monitoring:                Autoimmune disorders, such as Sjögren's syndrome (SS)        Cancers, such as ovarian cancer, breast cancer, prostate cancer, and oral squamous cell carcinoma        Cardiovascular diseases, such as atherosclerosis        Diabetes        Drugs, including anti-epileptic drugs; psychiatric medicines; and illicit drugs such as lithium, carbamazepine, cotinine, amphetamines, barbiturates, cannabinoids, cocaine, diazepines, ethanol, opioids, and phencyclidine        Hereditary diseases, such as 21-Hydroxylase deficiency        Hormone levels, such as for aldosterone, cortisol, dehydroepiandrosterone, estradiol, estriol, human chorionic gonadotropin (hcG), progesterone, and testosterone        Infectious diseases, such as brucellosis, Chlamydia, Helicobacter pylori infection, Leptospirosis, Lyme disease, neurocysticerosis, pigeon breeder's disease (PBD), schistosomiasis, and shigellosis        Oral health, such as oral candidiasis, oral bacteria monitoring, and periodontal disease        Psychiatric therapy, such as monitoring therapeutic responses to the treatment of anxiety and measuring post-traumatic stress disorder (PTSD)        Renal disease        Vaccination confirmation, such as for anthrax        Viral diseases, such as cytomegalovirus (CMV); dengue; Epstein-Barr virus (EBV); hepatitis A, B, and C; human herpes virus 6, 7, and 8; human immunodeficiency virus (HIV); human rabies; measles; mumps; rotavirus (RV); and rubella        
Rapid lateral flow assay devices also have established applications for food contaminant and environmental pollutant testing. Published scientific literature has demonstrated the use of lateral flow assays for detecting antibiotics, pesticides, bacteria, and viruses in food products such as fruits, plants, vegetables, grains, milk, eggs, meat, and animal feed. In addition, various published scientific literatures have demonstrated the application of rapid lateral flow assays for testing substances on the surfaces of objects (4-6, U.S. Patent Application No. 20070286771). Recent developments include allergen detection such as fungal a-amylase, a flour allergen commonly responsible for asthma, and mite allergens; and the detection of biothreat agents such as Baccilis anthracis, the etiologic agent of anthrax, and explosive residue, on contaminated surfaces. Food preparation and medical facilities have also implemented the use of rapid lateral flow assays that screen surfaces for Adenosine triphosphate (ATP) to examine if such surfaces are clean and free from microorganisms (U.S. Pat. No. 5,905,029).
Though many different applications have been demonstrated, drugs of abuse (DOA) testing is one of the most universal implementations for the rapid lateral flow assay. DOA testing is currently a multi-billion-dollar industry exhibiting significant market growth due to the increase in illicit drug use, the emergence of new drugs, and the rise in awareness of societal and personal consequences associated with illicit drug use. Main consumers consist of medical clinics; law enforcement; and employers that perform pre-employment screening, random employee testing, and/or government-mandated DOA testing. DOA testing consists of assays that test human urine, saliva, and blood for illicit substances. Although oral fluid testing has obvious advantages over urine and blood testing, the DOA testing market is dominated by the use of rapid lateral flow assays that test urine samples. The primary benefit of oral testing is its ability to negate privacy concerns. Saliva testing is comparable to conducting an oral temperature reading with a thermometer in that sample collection is performed face-to-face, leaving little to no chance of sample adulteration by the drug user. Oral fluid testing can also detect parent tetrahydrocannabinol (THC) in saliva, which is of great significance since parent THC presence indicates present drug influence. Other benefits include user-friendliness, convenience for on-site testing, non-invasiveness, and the ability to repeat sampling. Equally important is the close correlation of drug concentrations in oral fluid to that in blood (2, 7, 8).
Saliva is a unique bodily fluid and its popularity as a diagnostic medium has advanced exponentially in the last 10 years. In the United States, the need for further research in salivary diagnostics has been emphasized by federal action plans emanating from the Office of the Surgeon General [Health and Human Services (HHS), 2009] and the National Institute of Dental and Craniofacial Research (NIDCR, 2009). The literature is replete with over 2,500 articles since 1982, describing the use of saliva, gingival crevicular fluid, and mucosal transudates for drug monitoring and for the detection of various oral and systemic maladies.
While oral fluid rapid DOA testing has obvious merits, technical obstacles that limit its broad applications still exist today. For instance, the duration of sample collection with currently available collection devices can be too time-consuming due to the variable nature of saliva attributable to viscosity, mouth dryness, age, gender, and time of saliva collection (9). Collecting a sufficient volume of oral fluid for conducting a test run may take more than 5 minutes, yet in many cases collecting a sufficient sample volume can be unfeasible. Indeed, the necessary volume for a sample to mix and bind to its ligand in a lateral flow assay is often as little as less than 0.05 milliliters; however, this volume is not sufficient to maintain the capillary flow required to complete the test run.
Assaying a sample with an insufficient volume on a conventional lateral flow device can produce invalid results as the sample will not have the ability to run to completion. When a sufficient volume of a sample is unattainable or a only a small volume of a sample of interest remains, a test administrator may opt to dilute the sample in order to meet the larger sample volume requirements of a conventional lateral flow device. Nevertheless, screening a diluted sample can cause inaccurate test results as the concentration of the target analyte(s) may have been significantly diluted to an undetectable range. This can increase the chance of obtaining a false negative result, which can have serious ramifications for any type of screening. Conventional rapid lateral flow devices that test dry or solid samples, such as those from object surfaces, usually contain a reagent or solution that is directly added to the sample or preloaded onto the sample collecting component so that the dry or solid substance will be diluted in the solution.
With the growth of advanced applications for rapid lateral flow assays, it is clear that there is an unmet need for a rapid lateral flow device that is capable of testing small volume liquid samples as well as dry or solid samples while maintaining sample integrity.